Risk factors for COVID-19

Bulletin 23

Very little ‘multivariate’ analysis has been done to quantify the effect of COVID-19 risk factors simultaneously. Hence there is potential to misunderstand the operation of risk factors because of confounding – where the effect of one risk factor is distorted by the effect of another.

Age and biological sex are clearly risk factors. Obesity, hypertension and medical conditions such as diabetes appear to be risk factors, but their effect has been exaggerated in much commentary because they are strongly correlated with age and sex. Ethnicity also appears to be a risk factor. The evidence regarding smoking is unclear.

​COVID-19 risk factors can operate at two levels: “morbidity”, the risk of developing a severe form of COVID-19, and “mortality”, the risk that someone already unwell due to COVID-19 then dies. Risk factor effects should be compared against normal (all-cause) mortality.

Understanding risk factors better can help with understanding the underlying pathogenesis, and with evaluating strategies to move beyond lockdown.